Soft handoff with interference cancellation in a wireless frequency hopping communication system

ABSTRACT

Techniques are provided to support soft handoff in a frequency hopping OFDMA system. Each sector concurrently supports “non-handoff” users and “soft-handoff” users. A non-handoff user communicates with only one sector, and a soft-handoff user communicates with multiple sectors simultaneously. Non-handoff users are assigned traffic channels by their sole sectors, and soft-handoff users are assigned traffic channels by their “serving” sectors. For each sector, the traffic channels assigned to the non-handoff users are orthogonal to one another and may or may not be orthogonal to the traffic channels assigned to the soft-handoff users. Each sector processes its received signal and recovers the data transmissions from the non-handoff users of that sector. Each sector then estimates the interference due to the non-handoff users and cancels the interference from the received signal. Each sector further processes its interference-canceled signal to recover the data transmissions from the soft-handoff users.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is Continuation Application of U.S. application Ser.No. 10/622,663, filed Jul. 17, 2003, now issued as U.S. Pat. No.7,254,158 entitled “Soft Handoff with Interference Cancellation in awireless Frequency Hopping Communication System” which claims priorityto U.S. Application Ser. No. 60/470,160 filed May 12, 2003 and entitled“Soft Handoff with Interference Cancellation in a Wireless FrequencyHopping Communication System.”

BACKGROUND

I. Field

The present invention relates generally to communication, and morespecifically to techniques for supporting soft handoff in a wirelessfrequency hopping communication system using interference cancellation.

II. Background

In a frequency hopping communication system, data is transmitted ondifferent frequency subbands in different time intervals, which may bereferred to as “hop periods”. These frequency subbands may be providedby orthogonal frequency division multiplexing (OFDM), othermulti-carrier modulation techniques, or some other constructs. Withfrequency hopping, the data transmission hops from subband to subband ina pseudo-random manner. This hopping provides frequency diversity andallows the data transmission to better withstand deleterious patheffects such as narrow-band interference, jamming, fading, and so on.

An orthogonal frequency division multiple access (OFDMA) system utilizesOFDM and can support multiple users simultaneously. For a frequencyhopping OFDMA system, a data transmission for a given user may be senton a “traffic” channel that is associated with a specific frequencyhopping (FH) sequence. This FH sequence indicates the specific subbandto use for the data transmission in each hop period. Multiple datatransmissions for multiple users may be sent simultaneously on multipletraffic channels that are associated with different FH sequences. TheseFH sequences may be defined to be orthogonal to one another so that onlyone traffic channel, and thus only one data transmission, uses eachsubband in each hop period. By using orthogonal FH sequences, themultiple data transmissions do not interfere with one another whileenjoying the benefits of frequency diversity.

An OFDMA system may be deployed with multiple cells, where a celltypically refers to the coverage area of a base station. A datatransmission on a given subband in one cell acts as interference toanother data transmission on the same subband in a neighboring cell. Torandomize inter-cell interference, the FH sequences for each cell aretypically defined to be pseudo-random with respect to the FH sequencesfor neighboring cells. By using pseudo-random FH sequences for differentcells, interference diversity is achieved and a data transmission for auser in one cell observes the average interference from the datatransmissions for other users in other cells.

In a multi-cell OFDMA system, it is desirable to support “soft handoff”,which is also referred to as “soft handover”. Soft handoff is a processwhereby a user communicates with multiple base stations simultaneously.Soft handoff can provide spatial diversity against deleterious patheffects via transmission of data to or from multiple base stations atdifferent locations. However, soft handoff is complicated when thesystem employs frequency hopping. This is because the FH sequences forone cell are pseudo-random (i.e., not orthogonal) with respect to the FHsequences for neighboring cells in order to randomize inter-cellinterference. A user in soft handoff with multiple base stations may beinstructed to use an FH sequence by a designated base station among themultiple base stations. The data transmission sent by the soft-handoffuser will be orthogonal to the data transmissions sent by other users ofthe designated base station, but will be pseudo-random with respect tothe data transmissions sent by users of other base stations. Thesoft-handoff user would cause interference to the users of the otherbase stations and would also receive interference from these users. Theinterference degrades the performance of all affected users, unless itis mitigated in some manner.

There is therefore a need in the art for techniques to support softhandoff in a frequency hopping OFDMA system.

SUMMARY

Techniques are provided herein to support soft handoff in a wirelesscommunication system (e.g., a frequency hopping OFDMA system). Each cellin the system may be partitioned into one or multiple sectors. Eachsector in the system may concurrently support a set of “non-handoff”users and a set of “soft-handoff” users. A non-handoff user is one whois communicating with only one sector (i.e., not in soft handoff). Asoft-handoff user is one who is communicating with multiple sectorssimultaneously.

For each sector, each non-handoff user of that sector is assigned atraffic channel by that sector and each soft-handoff user of that sectoris assigned a traffic channel by a “serving” or “anchor” sector for thesoft-handoff user. The serving sector for a soft-handoff user is adesignated sector among the multiple sectors with which the soft-handoffuser is in communication. For each sector, the traffic channels assignedto the non-handoff users of that sector are orthogonal to one anotherand may or may not be orthogonal to the traffic channels assigned to thesoft-handoff users of that sector, depending on whether or not thatsector is the serving sector for the soft-handoff users.

For each sector, the non-handoff users of that sector may bepower-controlled such that their data transmissions can be received anddecoded by that sector in the presence of interference from thesoft-handoff users of that sector as well as the interference from usersin other sectors. The soft-handoff users may also be power-controlledsuch that their data transmissions can be decoded by their sectors whileminimizing interference to the non-handoff users.

Each sector processes its received signal and recovers the datatransmissions from the non-handoff users of that sector. Once the datatransmissions from the non-handoff users have been decoded, each sectorestimates the interference due to the non-handoff users of that sectorand cancels the interference from the received signal. Each sectorfurther processes its interference-canceled signal to recover the datatransmissions from the soft-handoff users of that sector.

Various aspects and embodiments of the invention are described infurther detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, nature, and advantages of the present invention willbecome more apparent from the detailed description set forth below whentaken in conjunction with the drawings in which like referencecharacters identify correspondingly throughout and wherein:

FIG. 1 shows an OFDMA system;

FIG. 2 illustrates frequency hopping for one sector in the OFDMA system;

FIG. 3 shows a block diagram of a terminal;

FIG. 4A shows a block diagram of a base station in a synchronous system;

FIG. 4B shows a block diagram of a base station in an asynchronoussystem;

FIG. 5 shows a block diagram of a receive (RX) data processor within thebase station in the synchronous system;

FIG. 6 shows a block diagram of an interference estimator and aninterference canceller within the RX data processor;

FIG. 7 shows a block diagram of an OFDM demodulator/RX data processorwithin the base station in the asynchronous system;

FIG. 8 shows a block diagram of an interference estimator and aninterference canceller within the OFDM demodulator/RX data processor;

FIG. 9 shows a flow diagram for transmitting data by the terminal; and

FIG. 10 shows a flow diagram for receiving data transmissions frommultiple terminals by the base station.

DETAILED DESCRIPTION

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any embodiment or design described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments or designs.

FIG. 1 shows an exemplary OFDMA system 100 that supports a number ofusers. System 100 includes a number of base stations 110 that providecommunication for a number of terminals 120. A base station is a fixedstation used for communicating with the terminals and may also bereferred to as an access point, a Node B, or some other terminology.Terminals 120 are typically dispersed throughout the system, and eachterminal may be fixed or mobile. A terminal may also be referred to as amobile station, a user equipment (UE), a wireless communication device,or some other terminology.

Each terminal may communicate with one or multiple base stations on theforward link and/or one or multiple base stations on the reverse link atany given moment. This depends on whether or not the terminal is active,whether or not soft handoff is supported, and whether or not theterminal is in soft handoff. The forward link (i.e., downlink) refers tothe communication link from the base station to the terminal, and thereverse link (i.e., uplink) refers to the communication link from theterminal to the base station. In FIG. 1, terminal 120 c is in softhandoff on the reverse link with base stations 110 a, 110 b, and 110 c,terminal 120 d is in soft handoff with base stations 110 a and 110 c,and terminal 120 g is in soft handoff with base stations 110 b and 110c. The remaining terminals are not in soft handoff. For simplicity,forward link transmissions are not shown in FIG. 1.

A system controller 130 couples to base stations 110 and may perform anumber of functions such as (1) coordination and control for basestations 110, (2) routing of data among these base stations, and (3)access and control of the terminals served by these base stations.

Each base station (e.g. 110 a, 110 b, and 110 c) provides coverage for arespective geographic area (e.g. 102 a, 102 b and 102 c). The term“cell” can refer to a base station and/or its coverage area, dependingon the context in which the term is used. To increase capacity, thecoverage area of each base station may be partitioned into multiplesectors (e.g., three sectors 104 a, 104 b, and 104 c). Each sector maybe served by a corresponding base transceiver subsystem (BTS). The term“sector” can refer to a BTS and/or its coverage area, depending on thecontext in which the term is used. For a sectorized cell, the basestation for that cell typically includes the BTSs for all of the sectorsof that cell. The following description assumes that each cell ispartitioned into multiple sectors. For simplicity, in the followingdescription, the term “base station” is used generically for both afixed station that serves a cell and a fixed station that serves asector. The base stations for all sectors of the same cell are typicallyimplemented within one physical base station for that cell.

The techniques described herein may be used to support soft handoff,whereby a terminal concurrently communicates with multiple cells. Thebase stations for these cells are included in the terminal's active set.These techniques may also be used to support “softer handoff”, which isa process whereby a terminal concurrently communicates with multiplesectors of the same cell. The base stations for these sectors (which aretypically parts of the same physical base station) are included in theterminal's active set. For simplicity, in the following description, theterm “soft handoff” generically refers to the case in which a terminalconcurrently communicates with multiple cells as well as the case inwhich a terminal concurrently communicates with multiple sectors of thesame cell.

The techniques described herein may be used for a synchronous system inwhich the timings of the base stations in the system are synchronized toa common clock source (e.g., GPS). These techniques may also be used foran asynchronous system in which the timings of the base stations in thesystem are not synchronized. For clarity, various details are describedbelow for a synchronous system. Moreover, the primary users for eachsector (defined below) are assumed to be synchronized with the basestation for the sector.

OFDMA system 100 utilizes OFDM, which is a modulation technique thateffectively partitions the overall system bandwidth into a number of (N)orthogonal frequency subbands, where N>1 and is typically a power oftwo. These subbands are also commonly referred to as tones,sub-carriers, bins, and frequency subchannels. With OFDM, each subbandis associated with a respective sub-carrier that may be modulated withdata. In some OFDM systems, only N_(D) subbands are used for datatransmission, N_(P) subbands are used for pilot transmission, and N_(G)subbands are not used and serve as guard subbands to allow the systemsto meet spectral mask requirements, where N=N_(D)+N_(P)+N_(G). Forsimplicity, the following description assumes that all N subbands can beused for data transmission.

FIG. 2 illustrates frequency hopping for one sector in the OFDMA system.Frequency hopping may be used to obtain various benefits includingfrequency diversity against deleterious path effects and interferencerandomization, as described above. For this example, N=8, and the eightsubbands are assigned indices of 1 through 8. Up to eight trafficchannels may be defined whereby each traffic channel uses one of theeight subbands in each hop period. A hop period may be defined to beequal to the duration of one or multiple OFDM symbols.

Each traffic channel is associated with a different FH sequence. The FHsequences for all traffic channels in the sector may be generated basedon an FH function ƒ_(s) (k,T), where k denotes the traffic channelnumber or identifier (ID) and T denotes system time, which is given inunits of hop periods. N different FH sequences may be generated with Ndifferent values of k in the FH function ƒ_(s), (k,T). The FH sequencefor each traffic channel indicates the specific subband to use for thattraffic channel in each hop period.

FIG. 2 shows the subbands used for two traffic channels 1 and 4. The FHsequence and subbands for traffic channel 1 are represented by theshaded boxes. The FH sequence and subbands for traffic channel 4 arerepresented by the diagonal-hashed boxes. It can be seen in FIG. 2 thateach traffic channel dynamically hops from subband to subband in apseudo-random manner determined by its FH sequence. In this example, theFH sequence for traffic channel 4, ƒ_(s) (4,T), is a vertically shiftedversion of the FH sequence for channel 1, ƒ_(s) (1,T). The subbands usedfor traffic channel 4 are related to the subbands used for trafficchannel 1 as follows:ƒ_(s)(4,T)=(ƒ_(s)(1,T)+3)mod N.

To avoid intra-sector interference, each sector may use orthogonal FHsequences for its traffic channels. The FH sequences are orthogonal toone another if no two FH sequences use the same subband in any hopperiod T. This orthogonality condition may be attained by defining theFH sequences for each sector to be vertically shifted versions of oneanother, as shown in FIG. 2. The traffic channels for each sector wouldthen be orthogonal to one another because they are associated withorthogonal FH sequences. By allowing only one traffic channel to useeach subband in each hop period, interference is avoided among multipledata transmissions sent on multiple traffic channels in the same sector.

For a multi-sector OFDMA system, data transmissions for users in onesector interfere with data transmissions for users in other sectors. Torandomize inter-sector interference, pseudo-random FH functions may beused for different sectors. For example, the FH function ƒ_(s) ₁ (k,T)for sector s₁ may be defined to be pseudo-random with respect to the FHfunction ƒ_(s) ₂ (m,T) for sector s₂. In this case, the FH sequence usedby sector s₁ for traffic channel k will be pseudo-random with respect tothe FH sequence used by sector s₂ for traffic channel m, where k may ormay not be equal to m. Interference between traffic channels k and moccurs whenever a “collision” occurs between the FH sequences for thesetraffic channels, i.e., whenever ƒ_(s) ₁ (k,T)=ƒ_(s) ₂ (m,T) and trafficchannels k and m both use the same subband in the same hop period.However, the interference will be randomized due to the pseudo-randomnature of the FH functions ƒ_(s) ₁ (k,T) and ƒ_(s) ₂ (m,T).

The FH sequences for each sector may thus be defined to be:

-   1. Orthogonal to each other to avoid intra-sector interference, and-   2. Pseudo-random with respect to the FH sequences for neighboring    sectors to randomize inter-sector interference.    With the above constraints, a user assigned with traffic channel k    by one sector will be orthogonal to all other users assigned with    other traffic channels by the same sector. However, this user will    not be orthogonal to all users in a neighboring sector, which uses a    different FH function.

Referring back to FIG. 1, each sector concurrently supports a set ofnon-handoff users and a set of soft-handoff users. Each user maycommunicate with one or multiple sectors, depending on whether or notthe user is in soft handoff. The sector or sectors with which a usercurrently communicates are included in an “active set”. For anon-handoff user, the active set includes a single sector, which is theserving sector for that user. For a soft-handoff user, the active setincludes multiple sectors, and one of these sectors (e.g., the strongestreceived sector) is designated as the serving sector for thesoft-handoff user.

The non-handoff users of each sector are assigned traffic channels withorthogonal FH sequences by that sector and thus do not interfere witheach other. Each soft-handoff user is assigned a traffic channel by itsserving sector. Each soft-handoff user is orthogonal to, and does notinterfere with, other users in its serving sector. However, eachsoft-handoff user will not be orthogonal to other users in other sectorsin its active set. Thus, the soft-handoff users of each sector may ormay not interfere with the non-handoff users of that sector. Thisdepends on whether the soft-handoff users have been assigned trafficchannels by that sector or by some other sectors.

For each sector, the non-handoff users of that sector may bepower-controlled such that their data transmissions can be decoded bythat sector in the presence of interference from the soft-handoff usersof that sector as well as interference from the users in other sectors.The soft-handoff users may also be power-controlled such that their datatransmissions can be decoded by the sectors in their active sets whileminimizing interference to the non-handoff users.

In one embodiment, each sector processes its received signal andrecovers the data transmissions from the non-handoff users of thatsector. Each sector then estimates the interference due to thenon-handoff users and cancels the interference from the received signal.Each sector further processes its interference-canceled signal torecover the data transmissions from the soft-handoff users of thatsector.

Each sector may also be viewed as concurrently supporting a set of“primary” users and a set of “secondary” users. For each sector, aprimary user is one who has been assigned a traffic channel by thatsector, and a secondary user is one who has been assigned a trafficchannel by another sector. The primary users of each sector include (1)non-handoff users of that sector and (2) soft-handoff users whoseserving sector is that sector. The secondary users of each sectorinclude soft-handoff users whose serving sectors are some other sectorsbesides that sector.

In another embodiment, each sector processes its received signal andrecovers the data transmissions from the primary users of that sector(which include non-handoff users of that sector as well as soft-handoffusers assigned traffic channels by that sector). Each sector thenestimates the interference due to the primary users and cancels theinterference from the received signal. Each sector further processes itsinterference-canceled signal to recover the data transmissions from thesecondary users of that sector (which are assigned traffic channels byother sectors).

Each sector may recover the data transmissions from the users in othermanners than the two embodiments described above, and this is within thescope of the invention. In general, it is desirable to cancel as muchinterference as possible. However, the ability to cancel theinterference due to a given user is dependent on the ability tocorrectly decode the data transmission from that user, which may in turnbe dependent on other factors such as, for example, the manner in whichthe user is power controlled.

FIG. 3 shows a block diagram of an embodiment of a terminal 120 x, whichis one of the terminals in OFDMA system 100. Terminal 120 x may be for anon-handoff user or a soft-handoff user. For simplicity, only thetransmitter portion of terminal 120 x is shown in FIG. 3.

Within terminal 120 x, an encoder/modulator 314 receives traffic datafrom a data source 312 and control data and other data from a controller330. The traffic data is designated for transmission on traffic channelx, which is assigned to terminal 120 x by the serving sector for theterminal. Encoder/modulator 314 formats, encodes, interleaves, andmodulates the received data and provides modulation symbols (or simply,“data symbols”). Each modulation symbol is a complex value for aspecific point in a signal constellation corresponding to the modulationscheme used for that modulation symbol.

A transmit frequency hopping (TX FH) switch 316 receives the datasymbols and provides these symbols onto the proper subbands for trafficchannel x. Traffic channel x is associated with FH sequence x, whichindicates the specific subband to use for traffic channel x in each hopperiod T. FH sequence x may be generated by controller 330 based on theFH function ƒ_(s) (k,T) for the serving sector. TX FH switch 316 mayalso provide pilot symbols on pilot subbands and further provides asignal value of zero for each subband not used for pilot or datatransmission. For each OFDM symbol period, TX FH switch 316 provides N“transmit” symbols (which are comprised of data symbols, pilot symbols,and zero-signal values) for the N subbands.

An OFDM modulator 318 receives the N transmit symbols for each OFDMsymbol period and provides a corresponding OFDM symbol. OFDM modulator318 typically includes an inverse fast Fourier transform (IFFT) unit anda cyclic prefix generator. For each OFDM symbol period, the IFFT unittransforms the N transmit symbols to the time domain using an N-pointinverse FFT to obtain a “transformed” symbol that contains N time-domain“chips”. Each chip is a complex value to be transmitted in one chipperiod. The cyclic prefix generator then repeats a portion of eachtransformed symbol to form an OFDM symbol that contains N+C_(p) chips,where C_(p) is the number of chips being repeated. The repeated portionis often referred to as a cyclic prefix and is used to combatinter-symbol interference (ISI) caused by frequency selective fading. AnOFDM symbol period corresponds to the duration of one OFDM symbol, whichis N+C_(p) chip periods. OFDM modulator 318 provides a stream of OFDMsymbols.

A transmitter unit (TMTR) 320 receives and processes the OFDM symbolstream to obtain a modulated signal. Transmitter unit 320 may furtheradjust the amplitude of the OFDM symbols and/or the modulated signalbased on a power control signal received from controller 330. Themodulated signal is transmitted from an antenna 322 to the basestation(s) in the active set for terminal 120 x.

FIG. 4A shows a block diagram of an embodiment of a base station 110 xin a synchronous OFDMA system. Base station 110 x is the fixed stationfor sector s_(x). For simplicity, only the receiver portion of basestation 110 x is shown in FIG. 4.

The modulated signals transmitted by the terminals within the coverageof base station 110 x are received by an antenna 412. The receivedsignal from antenna 412 may include (1) one or more modulated signalsfrom non-handoff users of sector s_(x) and (2) one or more modulatedsignals from soft-handoff users of sector s_(x). The received signal isprovided to and processed by a receiver unit (RCVR) 414 to obtainsamples. An OFDM demodulator 416 then processes the samples and provides“received” symbols, which are noisy estimates of the combined transmitsymbols sent by all terminals received by base station 110 x. OFDMdemodulator 416 typically includes a cyclic prefix removal unit and anFFT unit. For each OFDM symbol period, the cyclic prefix removal unitremoves the cyclic prefix in each received OFDM symbol to obtain areceived transformed symbol. The FFT unit then transforms each receivedtransformed symbol to the frequency domain with an N-point FFT to obtainN received symbols for the N subbands.

An RX data processor 420 obtains the N received symbols for each OFDMsymbol period and processes these symbols to obtain decoded data foreach terminal transmitting to base station 110 x. The processing by RXdata processor 420 is described in detail below. The decoded data foreach terminal may be provided to a data sink 422 for storage.

Controllers 330 and 430 direct the operation at terminal 120 x and basestation 110 x, respectively. Memory units 332 and 432 provide storagefor program codes and data used by controllers 330 and 430,respectively.

FIG. 4B shows a block diagram of an embodiment of a base station 110 yin an asynchronous OFDMA system. For an asynchronous system, the timingof the secondary users may be different from that of the primary users.An OFDM demodulator/RX data processor 440 performs OFDM demodulation foreach user based on that user's timing. OFDM demodulator/RX dataprocessor 440 also performs interference cancellation on time-domainsymbols, as described below.

The following description is for the embodiment whereby a primary userof sector s_(x) is one assigned a traffic channel by sector s_(x), and asecondary user of sector s_(x) is one assigned a traffic channel byanother sector besides sector s_(x). A primary user of sector s_(x) maybe a non-handoff user of sector s_(x) or a soft-handoff user of sectors_(x) whose serving sector is sector s_(x). A secondary user of sectors_(x) is a soft-handoff user of sector s_(x) whose serving sector isanother sector besides sector s_(x).

FIG. 5 shows a block diagram of an embodiment of RX data processor 420within base station 110 x in FIG. 4A for a synchronous OFDMA system. Inthis embodiment, RX data processor 420 includes P data processors 510 athrough 510 p for P primary users, an interference estimator 520, aninterference canceller 530, and S data processors 540 a through 540 sfor S secondary users, where P≧1 and S>1.

For each OFDM symbol period, OFDM demodulator 416 provides N receivedsymbols for the N subbands to data processors 510 a through 510 p andinterference canceller 530. One data processor 510 is assigned torecover the data transmission from each primary user. The processing bydata processor 510 a for a data transmission from primary user 1 isdescribed below. Primary user 1 is assigned traffic channel p1, which isassociated with FH sequence p1.

Within data processor 510 a, an RX FH switch 514 a receives the Nreceived symbols for the N subbands in each OFDM symbol period. RX FHswitch 514 a provides received data symbols for traffic channel p1 to ademodulator (Demod)/decoder 516 a and received pilot symbols for primaryuser 1 to a channel estimator 518 a. Since traffic channel p1dynamically hops from subband to subband, RX FH switch 514 a operates inunison with TX FH switch 316 at the terminal for primary user p1 toextract the received data symbols from the proper subbands for trafficchannel p1. The FH sequence provided to RX FH switch 514 a is the sameFH sequence provided to TX FH switch 316 at the terminal for primaryuser 1. Moreover, the FH sequences are synchronized.

A channel estimator 518 a obtains received pilot symbols for primaryuser 1 from RX FH switch 514 a (as shown in FIG. 5) or from the receivedsymbols. Channel estimator 518 a then derives channel estimates forprimary user 1 based on the received pilot symbols. The channelestimates may include estimates for (1) the channel gain between theterminal for primary user 1 and base station 110 x for each subband usedfor data transmission, (2) the signal strength of the pilot receivedfrom primary user 1, and (3) possibly other measurements.

Demodulator/decoder 516 a may coherently demodulate the received datasymbols from RX FH switch 514 a with the channel estimates from channelestimator 518 a to obtain data symbol estimates for primary user 1.Demodulator/decoder 516 a further demodulates (i.e., symbol demaps),deinterleaves, and decodes the data symbol estimates to obtain decodedtraffic data for primary user 1. In general, the processing performed bythe units within base station 110 x for primary user 1 is complementaryto the processing performed by the corresponding units in the terminalfor this primary user.

Data processors 510 a through 510 p provide decoded traffic data andchannel estimates for primary users 1 through P, respectively.Interference estimator 520 receives the decoded traffic data and thechannel estimates for primary users 1 through P, estimates theinterference due to each of the P primary users, and providesinterference estimates for the P primary users to interference canceller530. Interference canceller 530 receives the N received symbols for theN subbands in each OFDM symbol period and the interference estimates forthe P primary users. For each OFDM symbol period, interference canceller530 determines the total interference due to the P primary users on eachof the N subbands, subtracts the total interference from the receivedsymbol for each subband, and provides N interference-canceled symbolsfor the N subbands. An exemplary design for interference estimator 520and interference canceller 530 is described below.

One data processor 540 is assigned to recover the data transmission fromeach secondary user. Each data processor 540 includes an RX FH switch544, a demodulator/decoder 546, and a channel estimator 548, whichoperate in similar manner as RX FH switch 514, demodulator/decoder 516,and channel estimator 518, respectively, within data processor 510.However, RX FH switch 544 within each data processor 540 is providedwith the N interference-canceled symbols instead of the N receivedsymbols for the N subbands. Moreover, RX FH switch 544 within each dataprocessor 540 operates in unison with the TX FH switch at the terminalfor the secondary user being recovered by that data processor. Dataprocessors 540 a through 540 s provide decoded traffic data (andpossibly channel estimates) for secondary users 1 through S,respectively.

FIG. 6 shows a block diagram of an embodiment of interference estimator520 and interference canceller 530 within RX data processor 420 in FIG.4A for a synchronous OFDMA system. In this embodiment, interferenceestimator 520 includes P per-terminal interference estimators 620 athrough 620 p for P primary users. One per-terminal interferenceestimator 620 is assigned to estimate the interference due to eachprimary user. The processing by per-terminal interference estimator 620a to estimate the interference due to primary user 1 is described below.

Within per-terminal interference estimator 620 a, an encoder/modulator622 a receives the decoded traffic data for primary user 1.Encoder/modulator 622 a then encodes, interleaves, and modulates thedecoded traffic data and provides data symbols. A TX FH switch 624 areceives the data symbols from encoder/modulator 622 a and providesthese symbols onto the proper subbands for traffic channel p1 assignedto primary user 1, as indicated by FH sequence p1 associated with thistraffic channel. TX FH switch 624 a may also provide pilot symbols onthe proper subbands. TX FH switch 624 a provides N transmit symbols forthe N subbands in each OFDM symbol period. In general, the processing byencoder/modulator 622 a and TX FH switch 624 a is the same as thatperformed by encoder/modulator 314 and TX FH switch 316, respectively,at the terminal for primary user 1.

A channel simulator 628 a simulates the effects of the communicationlink between base station 110 x and the terminal for primary user 1.Channel simulator 628 a receives the transmit symbols from TX FH switch624 a and the channel estimates for primary user 1. Channel simulator628 a then processes the transmit symbols with the channel estimates toobtain an estimate of the interference due to primary user 1. Forexample, channel simulator 628 a may multiply the transmit symbol oneach subband with a channel gain estimate for that subband to obtain aninterference component on that subband due to primary user 1.

The received symbols contain signal components for the symbolstransmitted by the primary users and the secondary users of sectors_(x). The interference estimate from channel simulator 628 a is thesignal component for the symbols transmitted by primary user 1. Theinterference estimate includes N interference components for the Nsubbands, where the interference component for any given subband may bezero if no data or pilot symbol is transmitted on that subband byprimary user 1.

Per-terminal interference estimators 620 a through 620 p process thedecoded traffic data for primary users 1 through P, respectively.Channel simulators 628 a through 628 p within per-terminal interferenceestimators 620 a through 620 p provide the interference estimates forprimary users 1 through P, respectively.

Interference canceller 530 includes N P-input summers 630 a through 630n and N 2-input summers 632 a through 632 n, i.e., one set of summers630 and 632 for each of the N subbands. Interference canceller 530receives the N received symbols for the N subbands from OFDM demodulator416 and the interference estimates for primary users 1 through P fromper-terminal interference estimators 620 a through 620 p, respectively.Within interference canceller 530, summer 630 a receives and sums theinterference components on subband 1 due to the P primary users andprovides the total interference on subband 1. Each of the other N−1summers 630 for subbands 2 through N similarly receives and sums theinterference components on the associated subband due to the P primaryusers and provides the total interference on that subband. Summer 632 areceives and subtracts the total interference on subband 1 from thereceived symbol for subband 1 and provides the interference-canceledsymbol for subband 1. Each of the other N−1 summers 632 for subbands 2through N similarly receives and subtracts the total interference on theassociated subband from the received symbol for that subband andprovides the interference-canceled symbol for that subband. Summers 632a through 632 n provide the N interference-canceled symbols for the Nsubbands for each OFDM symbol period.

FIG. 7 shows a block diagram of an embodiment of OFDM demodulator/RXdata processor 440 within base station 110 y in FIG. 4B for anasynchronous OFDMA system. In this embodiment, OFDM demodulator/RX dataprocessor 440 includes P data processors 710 a through 710 p for Pprimary users, an interference estimator 720, an interference canceller730, and S data processors 740 a through 740 s for S secondary users,where P≧1 and S≧1.

The recovered symbols from receiver unit 414 are provided to each ofdata processors 710 a through 710 p. Each data processor 710 includes anOFDM demodulator 712, an RX FH switch 714, a demodulator/decoder 716,and a channel estimator 718. OFDM demodulator 712 within each dataprocessor 710 performs OFDM demodulation on the received symbols basedon the timing of the primary user assigned to that data processor andprovides symbol estimates for the N subbands. RX FH switch 714,demodulator/decoder 716, and channel estimator 718 then operate on thesymbol estimates in similar manner as described above in FIG. 5 for RXFH switch 514, demodulator/decoder 516, and channel estimator 518,respectively. Each data processor 740 also includes an OFDM demodulator742 that performs OFDM demodulation on the interference-canceled symbolsbased on the timing of the secondary user assigned to that dataprocessor.

FIG. 8 shows a block diagram of an embodiment of interference estimator720 and interference canceller 730 within OFDM demodulator/RX dataprocessor 440 in FIG. 4B for an asynchronous OFDMA system. In thisembodiment, interference estimator 720 includes P per-terminalinterference estimators 820 a through 820 p for P primary users. Oneper-terminal interference estimator 820 is assigned to estimate theinterference due to each primary user. Each per-terminal interferenceestimator 820 includes an encoder/modulator 822, a TX FH switch 824, anOFDM modulator 826, and a channel simulator 828. Encoder/modulator 822and TX FH switch 824 operate as described above in FIG. 6 forencoder/modulator 622 and TX FH switch 624, respectively. TX FH switch824 provides N transmit symbols for the N subbands in each OFDM symbolperiod. OFDM modulator 826 then performs OFDM modulation on the Ntransmit symbols for each OFDM symbol period and provides time-domainsymbols.

Channel simulator 828 then processes the time-domain symbols with thechannel estimates for the assigned primary user to obtain an estimate ofthe interference due to the primary user. Since different primary usersmay be associated with different timing for an asynchronous system,channel simulator 828 also performs sample rate conversion so that theinterference estimate from the channel simulator is time-aligned withthe received symbols.

Interference canceller 730 includes a P-input summer 830 and a 2-inputsummer 832. Interference canceller 730 receives the received symbolsfrom receiver unit 414 and the interference estimates for primary users1 through P from per-terminal interference estimators 820 a through 820p, respectively. Within interference canceller 730, summer 830 sums theinterference due to the P primary users and provides the totalinterference. Summer 832 subtracts the total interference from thereceived symbols and provides the interference-canceled symbols, whichare processed by data processors 740 a through 740 s for the S secondaryusers.

The embodiment shown in FIGS. 5 and 6 suggests that the interference dueto all P primary users is estimated and canceled prior to recovering thedata transmissions from the S secondary users. A primary user of sectors_(x) may be a soft-handoff user who is power-controlled by multiplesectors in that user's active set. Base station 110 x for sector s_(x)may not be able to decode the data transmission from this primary userif it is power-controlled such that it can be recovered by othersector(s) in the active set. If the data transmission from any primaryuser cannot be decoded, then base station 110 x may not attempt toestimate and cancel the interference due to that primary user. A basestation may use partially decoded data to cancel some of theinterference.

The description above for FIGS. 5 and 6 also applies to an embodimentwhereby a primary user of sector s_(x) is a non-handoff user of sectors_(x), and a secondary user of sector s_(x) is a soft-handoff user ofsector s_(x) (regardless of the serving sector for the soft-handoffuser).

For the embodiment shown in FIGS. 5 and 6, the primary users are decodedfirst and the secondary users are decoded next, after the interferencedue to the primary users have been estimated and canceled. It may alsobe possible to decode the secondary users first and then the primaryusers next, after the interference due to the secondary users have beenestimated and canceled. In general, the data transmissions from usersmay be decoded in any order by base station 110 x. The interference dueto each successfully decoded user may be estimated and canceled toimprove the signal quality of remaining, not yet decoded users. However,system implementation may be simplified if non-handoff users arepower-controlled such that they can be successfully decoded in thepresence of interference from soft-handoff users. In this case, thenon-handoff users are decoded first followed by the soft-handoff users.

For simplicity, FIGS. 5 and 6 show a parallel design whereby (1) onedata processor 510 and one per-terminal interference estimator 620 isprovided for each primary user and (2) one data processor 540 isprovided for each secondary user. A time division multiplex (TOM) designmay also be used whereby one data processor 510 is provided andtime-shared for all primary and secondary users and one per-terminalinterference estimator 620 is also provided and time-shared for allprimary users.

FIG. 9 shows a flow diagram of a process 900 for transmitting data in awireless communication system (e.g., a frequency hopping OFDMA system).Process 900 may be performed by each terminal that is in soft handoffwith multiple base stations for multiple sectors.

Initially, an assignment of a traffic channel is obtained from a firstbase station (step 912). For a frequency hopping OFDMA system, theassigned traffic channel is associated with an FH sequence thatindicates the specific subband to use for data transmission in each timeinterval (i.e., each hop period). Data is encoded and modulated toobtain data symbols (step 914). For a frequency hopping OFDMA system,the data symbols are provided on the subbands indicated by the FHsequence (step 916). The data symbols are further processed (e.g., OFDMmodulated) for transmission on the assigned traffic channel to the firstbase station and to a second base station (step 918).

Traffic channels assigned by the first base station are orthogonal toone another and are not orthogonal to traffic channels assigned by thesecond base station. For a frequency hopping OFDMA system, the trafficchannels assigned by the first and second base stations are eachassociated with a respective FH sequence. The FH sequences for thetraffic channels assigned by the first base station are orthogonal toone another and are not orthogonal to the FH sequences for the trafficchannels assigned by the second base station.

FIG. 10 shows a flow diagram of a process 1000 for receiving datatransmissions from multiple terminals in a wireless communication system(e.g., a frequency hopping OFDMA system). Process 1000 may be performedby the base station for each sector. For clarity, the processing by basestation x for sector s_(x) is described below.

Initially, received symbols are obtained (step 1012). The receivedsymbols include (1) at least one data transmission on at least one“primary” traffic channel from at least one primary terminal and (2) atleast one data transmission on at least one “secondary” traffic channelfrom at least one secondary terminal. Primary traffic channels are thoseassigned by base station x, and secondary traffic channels are thoseassigned by other base stations (e.g., neighboring base stations of basestation x). The primary traffic channels are orthogonal to one anotherand are not orthogonal to the secondary traffic channels. The primarytraffic channels may be pseudo-random with respect to the secondarytraffic channels. Primary terminals are those assigned primary trafficchannels by base station x, and secondary terminals are those assignedsecondary traffic channels by other base stations. Each secondaryterminal may be in soft handoff with at least two base stations (whichinclude base station x) and may be assigned a secondary traffic channelby another base station other than base station x.

For an OFDMA system, the received symbols are obtained for N subbandsfrom an OFDM demodulator. Also for an OFDMA system, each traffic channelis associated with a respective FH sequence. The “primary” FH sequencesfor the primary traffic channels are orthogonal to one another and arenot orthogonal to “secondary” FH sequences for the secondary trafficchannels.

The received symbols are processed to obtain decoded data for eachprimary terminal (step 1014). Interference due to the primaryterminal(s) is estimated (step 1016) and canceled from the receivedsymbols to obtain interference-canceled symbols (step 1018). Theinterference-canceled symbols are then processed to obtain decoded datafor each secondary terminal (step 1020).

The processing for each primary terminal may include (1) obtaining thereceived symbols on the subbands indicated by the primary FH sequencefor the primary traffic channel assigned to the primary terminal, (2)deriving channel estimates for the primary terminal (e.g., based onpilot symbols received from the primary terminal), and (3) demodulatingand decoding the received symbols for the primary terminal (e.g., withthe channel estimates for the primary terminal) to obtain the decodeddata for the primary terminal. The processing for each secondaryterminal may be performed in similar manner, albeit on theinterference-canceled symbols instead of the received symbols.

The interference due to each primary terminal may be estimated by (1)encoding and modulating the decoded data for the primary terminal toobtain data symbols, (2) providing the data symbols on the subbandsindicated by the FH sequence assigned to the primary terminal, and (3)processing the data symbols with the channel estimates to obtain theinterference due to the primary terminal. The interference due to eachprimary terminal may be combined to obtain total interference due to theprimary terminal(s).

The techniques described herein may be used for a frequency hoppingOFDMA system as well as other types of wireless communication systems.For example, these techniques may be used for systems that employ othermulti-carrier modulation techniques, such as discrete multi-tone (DMT).These techniques may also be used for wireless communication systemsthat do not employ multi-carrier modulation and those that do not employfrequency hopping.

The techniques described herein may be used for systems that definetraffic channels in some other manners. For a frequency hopping OFDMAsystem, a traffic channel is defined by an associated FH sequence, whichindicates the specific subband to use in each hop period. For a timedivision multiplex (TDM) system, data may be transmitted in time slots,and multiple traffic channels may be assigned different time slots. Thetraffic channels for each sector may be defined to be orthogonal to oneanother so that no two traffic channels use the same time slot. Thetraffic channels for different sectors may be pseudo-random so that atraffic channel for one sector may use the same time slot as (and thuscollide with) a traffic channel for another sector. The techniquesdescribed herein may also be used for this TDM system. Each soft-handoffuser is assigned one traffic channel by its serving sector. Each sectorwould recover the data transmissions from the primary users of thatsector, cancel the interference due to the primary users, and thenrecover the data transmissions from the secondary users of that sector.

The techniques described herein may be used to support soft handoff onthe reverse link, as described above. These techniques may also be usedto support softer handoff, which is a process whereby a terminalcommunicates with multiple sectors of the same cell. The same processingmay be performed at the base station and the terminal for both softhandoff and softer handoff.

The techniques described herein may also be used for the forward link.For example, a terminal may simultaneously receive a user-specific datatransmission from one base station and overhead transmissions (e.g.,broadcast transmissions) from multiple base stations on the forwardlink. The terminal may process its received signal to recover theuser-specific data transmission from the one base station, estimate andcancel the interference due to the user-specific data transmission, andprocess the interference-canceled signal to recover the overheadtransmissions from the multiple base stations.

The techniques described herein may be implemented by various means. Forexample, these techniques may be implemented in hardware, software, or acombination thereof. For a hardware implementation, the processing units(e.g., data processors 510 and 540, interference estimator 520,interference canceller 530, and so on) within a base station may beimplemented within one or more application specific integrated circuits(ASICS), digital signal processors (DSPS), digital signal processingdevices (DSPDs), programmable logic devices (PLDs), field programmablegate arrays (FPGAs), processors, controllers, micro-controllers,microprocessors, other electronic units designed to perform thefunctions described herein, or a combination thereof. The processingunits (e.g., encoder/modulator 314, TX FH switch 316, OFDM modulator318, and so on) within a terminal may also be implemented within one ormore BASICS, DSPs, and so on.

For a software implementation, the techniques described herein may beimplemented with modules (e.g., procedures, functions, and so on) thatperform the functions described herein. The software codes may be storedin memory units (e.g., memory units 332 and 432 in FIGS. 3 and 4) andexecuted by processors (e.g., controllers 330 and 430). The memory unitmay be implemented within the processor or external to the processor, inwhich case it can be communicatively coupled to the processor viavarious means as is known in the art.

The previous description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

What is claimed is:
 1. A method of transmitting data from a terminal ina wireless communication system, comprising: receiving traffic data andcontrol data, the control data comprising at least an assignment of aprimary traffic channel from one of first and second base stations and apower control signal, the primary traffic channel being orthogonal to atleast one other primary traffic channel assigned by said one of thefirst and second base stations, the primary traffic channels beingpseudo-random relative to secondary traffic channels assigned by theother of said first and second base stations; encoding and modulatingthe received traffic data to obtain data symbols; and transmitting, by atransmitter, the data symbols on the assigned primary traffic channelcomprising adjusting at least an amplitude of the data symbols based onthe power control signal prior to a transmission of the data symbols;wherein, when the terminal is operating as a non-handoff usercommunicating with a first active set defined by the first base station,the primary traffic channel assignment is from the first base stationand said power control signal controls said adjusting to effect a firstsaid transmission adapted for a first objective that the first basestation can decode the transmitted data symbols in the presence ofinterference caused by other transmissions received at the first basestation, and estimate and cancel interference that the transmitted datasymbols cause to said other transmissions; wherein, when the terminal isoperating as a soft-handoff user communicating with a second active setthat includes at least the first and second base stations, the primarytraffic channel assignment is from the second base station and saidpower control signal controls said adjusting to effect a second saidtransmission adapted for a second objective that is different than thefirst objective.
 2. The method of claim 1, wherein the transmission fromthe terminal is operative to be received and processed by the first basestation prior to recovering transmissions from other terminals assignedwith other traffic channels not orthogonal to the primary trafficchannel assigned to the terminal.
 3. The method of claim 1, whereintransmissions from other terminals assigned with other traffic channelsby the second base station are received and processed by the second basestation prior to recovering the transmission from the terminal.
 4. Themethod of claim 1, wherein the wireless communication system is afrequency hopping communication system.
 5. The method of claim 4,wherein the primary traffic channel and the secondary traffic channelsare each associated with a respective frequency hopping (FH) sequencethat indicates a specific one of a plurality of subbands to use for datatransmission in each time interval.
 6. The method of claim 1, whereinthe first base station and the second base station correspond to twodifferent sectors of one cell in the system.
 7. The method of claim 1,wherein the first base station and the second base station correspond totwo different cells in the system.
 8. The method of claim 1, wherein thetransmission is only to the first base station.
 9. The method of claim1, wherein the transmission is only to a first sector of the first basestation.
 10. The method of claim 1, wherein the transmission is to bothof the first base station and the second base station.
 11. The method ofclaim 1, wherein the second objective is that the second base stationcan decode the transmitted data symbols, and interference, caused by thetransmitted data symbols to transmissions received at the base stationsin the second active set from non-handoff users having primary trafficchannels assigned by the base stations in the second active set, isminimized.
 12. A method of transmitting data from a terminal in awireless frequency hopping (FH) communication system, comprising:receiving traffic data and control data, the control data comprising atleast an FH sequence assigned by one of first and second base stationsand a power control signal, wherein the FH sequence is orthogonal to atleast one other FH sequence assigned by said one of the first and secondbase stations, and the FH sequence is not orthogonal to FH sequencesassigned by the other of said first and second base stations; encodingand modulating the received traffic data to obtain data symbols;providing the data symbols on subbands indicated by the assigned FHsequence comprising designating at least a portion of the subbands aszero signal subbands; and processing the data symbols into atransmission using the assigned FH sequence, comprising adjusting atleast an amplitude of the data symbols based on the power control signalprior to the transmission; wherein, when the terminal is operating as anon-handoff user communicating with a first active set defined by thefirst base station, the FH sequence is assigned by the first basestation and said power control signal controls said adjusting to effecta first said transmission adapted for a first objective that the firstbase station can decode the transmitted data symbols in the presence ofinterference caused by other transmissions received at the first basestation, and estimate and cancel interference that the transmitted datasymbols cause to said other transmissions; wherein, when the terminal isoperating as a soft-handoff user communicating with a second active setthat includes at least the first and second base stations, the FHsequence is assigned by the second base station and said power controlsignal controls said adjusting to effect a second said transmissionadapted for a second objective that is different than the firstobjective.
 13. The method of claim 12, wherein the FH sequences assignedby the first base station are pseudo-random with respect to the FHsequences assigned by the second base station.
 14. The method of claim12, wherein the transmission is operative to be received and processedby the first base station prior to recovering other transmissions fromterminals assigned with other FH sequences not orthogonal to the FHsequence assigned by the first base station.
 15. The method of claim 12,wherein the transmission is only to the first base station.
 16. Themethod of claim 12, wherein the transmission is only to a first sectorof the first base station.
 17. The method of claim 12, wherein thetransmission is to both of the first base station and the second basestation.
 18. The method of claim 12, wherein the second objective isthat the second base station can decode the transmitted data symbols,and interference, caused by the transmitted data symbols totransmissions received at the base stations in the second active setfrom non-handoff users having primary traffic channels assigned by thebase stations in the second active set, is minimized.
 19. An apparatusin a terminal in a wireless frequency hopping (FH) communication system,comprising: means for providing traffic data and control data, thecontrol data comprising at least an FH sequence assigned by one of firstand second base stations and a power control signal, wherein the FHsequence is orthogonal to at least one other FH sequence assigned bysaid one of the first and second base stations, and the FH sequence isnot orthogonal to FH sequences assigned by the other of said first andsecond base stations; means for encoding and modulating the traffic datato obtain data symbols; means for providing the data symbols on subbandsindicated by the assigned FH sequence comprising designating at least aportion of the subbands as zero signal subbands; and means forprocessing the data symbols into a transmission using the assigned FHsequence comprising adjusting at least an amplitude of the data symbolsbased on the power control signal prior to the transmission; wherein,when the terminal is operating as a non-handoff user communicating witha first active set defined by the first base station, the FH sequence isassigned by the first base station and said power control signalcontrols said adjusting to effect a first said transmission adapted fora first objective that the first base station can decode the transmitteddata symbols in the presence of interference caused by othertransmissions received at the first base station, and estimate andcancel interference that the transmitted data symbols cause to saidother transmissions; wherein, when the terminal is operating as asoft-handoff user communicating with a second active set that includesat least the first and second base stations, the FH sequence is assignedby the second base station and said power control signal controls saidadjusting to effect a second said transmission adapted for a secondobjective that is different than the first objective.
 20. The apparatusof claim 19, wherein the transmission is operative to be received andprocessed by the first base station prior to recovering othertransmissions from terminals assigned with other FH sequences notorthogonal to the FH sequence assigned by the first base station. 21.The apparatus of claim 19, wherein the transmission is only to the firstbase station.
 22. The apparatus of claim 19 wherein the transmission isonly to a first sector of the first base station.
 23. The apparatus ofclaim 19, wherein the transmission is to both of the first base stationand the second base station.
 24. The apparatus of claim 19, wherein thesecond objective is that the second base station can decode thetransmitted data symbols, and interference, caused by the transmitteddata symbols to transmissions received at the base stations in thesecond active set from non-handoff users having primary traffic channelsassigned by the base stations in the second active set, is minimized.25. An apparatus in a terminal in a wireless frequency hopping (FH)communication system, comprising: a controller operative to providecontrol data comprising at least an FH sequence assigned by one of firstand second base stations and a power control signal, wherein the FHsequence is orthogonal to at least one other FH sequence assigned bysaid one of the first and second base stations, and the FH sequence isnot orthogonal to FH sequences assigned by the other of said first andsecond base stations; an encoder and modulator operative to encode andmodulate traffic data to obtain data symbols; a switch operative toprovide the data symbols on subbands indicated by the assigned FHsequence comprising designating at least a portion of the subbands aszero signal subbands; and an orthogonal frequency division multiplexing(OFDM) modulator operative to process the data symbols into atransmission using the assigned FH sequence comprising adjusting atleast an amplitude of the data symbols based on the power control signalprior to the transmission; wherein, when the terminal is operating as anon-handoff user communicating with a first active set defined by thefirst base station, the FH sequence is assigned by the first basestation and said power control signal controls said adjusting to effecta first said transmission adapted for a first objective that the firstbase station can decode the transmitted data symbols in the presence ofinterference caused by other transmissions received at the first basestation, and estimate and cancel interference that the transmitted datasymbols cause to said other transmissions; wherein, when the terminal isoperating as a soft-handoff user communicating with a second active setthat includes at least the first and second base stations, the FHsequence is assigned by the second base station and said power controlsignal controls said adjusting to effect a second said transmissionadapted for a second objective that is different than the firstobjective.
 26. The apparatus of claim 25, wherein the transmission isoperative to be received and processed by the first base station priorto recovering other transmissions from terminals assigned with other FHsequences not orthogonal to the FH sequence assigned by the first basestation.
 27. The apparatus of claim 25, wherein the transmission is onlyto the first base station.
 28. The apparatus of claim 25, wherein thetransmission is only to a first sector of the first base station. 29.The apparatus of claim 25, wherein the transmission is to both of thefirst base station and the second base station.
 30. The apparatus ofclaim 25, wherein the second objective is that the second base stationcan decode the transmitted data symbols, and interference, caused by thetransmitted data symbols to transmissions received at the base stationsin the second active set from non-handoff users having primary trafficchannels assigned by the base stations in the second active set, isminimized.
 31. A non-transitory processor readable media for storinginstructions in a terminal that cause the terminal to: receive trafficdata and control data, the control data comprising at least a frequencyhopping (FH) sequence assigned by one of first and second base stationsand a power control signal, wherein the FH sequence is orthogonal to atleast one other FH sequence assigned by said one of the first and secondbase stations, and the FH sequence is not orthogonal to FH sequencesassigned by the other of said first and second base stations; encode andmodulate the received traffic data to obtain data symbols; provide thedata symbols on sub bands indicated by the assigned FH sequencecomprising designating at least a portion of the subbands as zero signalsubbands; and process the data symbols into a transmission using theassigned FH sequence comprising adjusting at least an amplitude of thedata symbols based on the power control signal prior to thetransmission; wherein, when the terminal is operating as a non-handoffuser communicating with a first active set defined by the first basestation, the FH sequence is assigned by the first base station and saidpower control signal controls said adjusting to effect a first saidtransmission adapted for a first objective that the first base stationcan decode the transmitted data symbols in the presence of interferencecaused by other transmissions received at the first base station, andestimate and cancel interference that the transmitted data symbols causeto said other transmissions; wherein, when the terminal is operating asa soft-handoff user communicating with a second active set that includesat least the first and second base stations, the FH sequence is assignedby the second base station and said power control signal controls saidadjusting to effect a second said transmission adapted for a secondobjective that is different than the first objective.
 32. The processorreadable media of claim 31, wherein the transmission is operative to bereceived and processed by the first base station prior to recoveringother transmissions from terminals assigned with other FH sequences notorthogonal to the FH sequence assigned by the first base station. 33.The processor readable media of claim 31, wherein the transmission isonly to the first base station.
 34. The processor readable media ofclaim 31, wherein the transmission is only to a first sector of thefirst base station.
 35. The processor readable media of claim 31,wherein the transmission is to both of the first base station and thesecond base station.
 36. The non-transitory processor readable media ofclaim 31, wherein the second objective is that the second base stationcan decode the transmitted data symbols, and interference, caused by thetransmitted data symbols to transmissions received at the base stationsin the second active set from non-handoff users having primary trafficchannels assigned by the base stations in the second active set, isminimized.
 37. An apparatus in a terminal in a wireless communicationsystem, comprising: a controller operative to provide control datacomprising at least an assignment of a primary traffic channel from oneof first and second base stations and a power control signal, theprimary traffic channel being orthogonal to at least one other primarytraffic channel assigned by said one of the first and second basestations, the primary traffic channels being pseudo-random relative tosecondary traffic channels assigned by the other of said first andsecond base stations; an encoder and modulator operative to encode andmodulate traffic data to obtain data symbols; and a transmitteroperative to transmit the data symbols on the assigned primary trafficchannel comprising adjusting at least an amplitude of the data symbolsbased on the power control signal prior to a transmission of the datasymbols; wherein, when the terminal is operating as a non-handoff usercommunicating with a first active set defined by the first base station,the primary traffic channel assignment is from the first base stationand said power control signal controls said adjusting to effect a firstsaid transmission adapted for a first objective that the first basestation can decode the transmitted data symbols in the presence ofinterference caused by other transmissions received at the first basestation, and estimate and cancel interference that the transmitted datasymbols cause to said other transmissions; wherein, when the terminal isoperating as a soft-handoff user communicating with a second active setthat includes at least the first and second base stations, the primarytraffic channel assignment is from the second base station and saidpower control signal controls said adjusting to effect a second saidtransmission adapted for a second objective that is different than thefirst objective.
 38. The apparatus of claim 37, wherein the transmissionfrom the terminal is operative to be received and processed by the firstbase station prior to recovering transmissions from other terminalsassigned with other traffic channels not orthogonal to the primarytraffic channel assigned to the terminal.
 39. The apparatus of claim 37,wherein transmissions from other terminals assigned with other trafficchannels by the second base station are received and processed by thesecond base station prior to recovering the transmission from theterminal.
 40. The apparatus of claim 37, wherein the wirelesscommunication system is a frequency hopping communication system. 41.The apparatus of claim 40, wherein the primary traffic channel and thesecondary traffic channels are each associated with a respectivefrequency hopping (FH) sequence that indicates a specific one of aplurality of subbands to use for data transmission in each timeinterval.
 42. The apparatus of claim 37, wherein the first base stationand the second base station correspond to two different sectors of onecell in the system.
 43. The apparatus of claim 37, wherein the firstbase station and the second base station correspond to two differentcells in the system.
 44. The apparatus of claim 37, wherein thetransmission is only to the first base station.
 45. The apparatus ofclaim 37, wherein the transmission is only to a first sector of thefirst base station.
 46. The apparatus of claim 37, wherein thetransmission is to both of the first base station and the second basestation.
 47. The apparatus of claim 37, wherein the second objective isthat the second base station can decode the transmitted data symbols,and interference, caused by the transmitted data symbols totransmissions received at the base stations in the second active setfrom non-handoff users having primary traffic channels assigned by thebase stations in the second active set, is minimized.
 48. Anon-transitory processor readable media for storing instructions in aterminal that cause the terminal to: receive traffic data and controldata, the control data comprising at least an assignment of a primarytraffic channel from one of first and second base stations and a powercontrol signal, the primary traffic channel being orthogonal to at leastone other primary traffic channel assigned by said one of the first andsecond base stations, the primary traffic channels being pseudo-randomrelative to secondary traffic channels assigned by the other of saidfirst and second base stations; encode and modulate the received trafficdata to obtain data symbols; and transmit the data symbols on theassigned primary traffic channel comprising adjusting at least anamplitude of the data symbols based on the power control signal prior toa transmission of the data symbols; wherein, when the terminal isoperating as a non-handoff user communicating with a first active setdefined by the first base station, the primary traffic channelassignment is from the first base station and said power control signalcontrols said adjusting to effect a first said transmission adapted fora first objective that the first base station can decode the transmitteddata symbols in the presence of interference caused by othertransmissions received at the first base station, and estimate andcancel interference that the transmitted data symbols cause to saidother transmissions; wherein, when the terminal is operating as asoft-handoff user communicating with a second active set that includesat least the first and second base stations, the primary traffic channelassignment is from the second base station and said power control signalcontrols said adjusting to effect a second said transmission adapted fora second objective that is different than the first objective.
 49. Thenon-transitory processor readable media of claim 48, wherein the secondobjective is that the second base station can decode the transmitteddata symbols, and interference, caused by the transmitted data symbolsto transmissions received at the base stations in the second active setfrom non-handoff users having primary traffic channels assigned by thebase stations in the second active set, is minimized.
 50. An apparatusin a terminal in a wireless communication system, comprising: means forproviding traffic data and control data, the control data comprising atleast an assignment of a primary traffic channel from one of first andsecond base stations and a power control signal, the primary trafficchannel being orthogonal to at least one other primary traffic channelassigned by said one of the first and second base stations, the primarytraffic channels being pseudo-random relative to secondary trafficchannels assigned by the other of said first and second base stations;means for encoding and modulating the traffic data to obtain datasymbols; and means for transmitting the data symbols on the assignedprimary traffic channel comprising adjusting at least an amplitude ofthe data symbols based on the power control signal prior to atransmission of the data symbols; wherein, when the terminal isoperating as a non-handoff user communicating with a first active setdefined by the first base station, the primary traffic channelassignment is from the first base station and said power control signalcontrols said adjusting to effect a first said transmission adapted fora first objective that the first base station can decode the transmitteddata symbols in the presence of interference caused by othertransmissions received at the first base station, and estimate andcancel interference that the transmitted data symbols cause to saidother transmissions; wherein, when the terminal is operating as asoft-handoff user communicating with a second active set that includesat least the first and second base stations, the primary traffic channelassignment is from the second base station and said power control signalcontrols said adjusting to effect a second said transmission adapted fora second objective that is different than the first objective.
 51. Theapparatus of claim 50, wherein the second objective is that the secondbase station can decode the transmitted data symbols, and interference,caused by the transmitted data symbols to transmissions received at thebase stations in the second active set from non-handoff users havingprimary traffic channels assigned by the base stations in the secondactive set, is minimized.